Direction finder



Oct. 2, 1928. 1,685,821

I A LEIB DIRECTION FINbER 7 Filed April 29, 1924 6 Shets-Sheet 1anoentoz AueusT' LEIB 1 Oct. 2, 1928. 1,685,821

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0d. 2, 1923. 1 685321 A. LE IB 1 DIRECTION FINDER Filed April 29, 1%; 6Sheets-Sheet 4 Elk wanton AUGU ST LEIB A; LEiB DiRECTION FINDER FiledApril 29, 1924 4 {sheetsshew '5,-

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DIRECTION mush Filed Apx ii 29, "1924 6 Sheets-shad "6;

y, ;-v n m I I AUGUST L618 Patented j 062. 2, i928.

nueusr LEIB, or B RLI teams, Assmuon. 'ro GEsEnLscHArr run. DRAKE-LOSE'rnnnemmn 12:. 12. 1,01 BERLIN, ennmmvma CORPORATION orennmm. I

a lication filed A1111l29, i924, Serial re 709,819, andin Germany am19', 1923.

' This invention relates to means for finds .ing the direction of astation transmitting -'wi reless'signals and moreparticularl'y to a"deviceof this'kindemploying a .rotatable 6 loop aerial in'conj'unctionwitha fixed undi rectional aerial. I 3 object of the inventionis toprovide a device which will poi'ntaccur'atel-y in the direction of thetransmitting station under flallconditions of wave front so long as thedirection of wave propagation continues in .a straight line. A furtherobject of. the invention is to provide a device which will provide adistinct-minimum in the detectmg apparatus when the axis of the loopis'in line with the transmitter; A further ob- 'ject is to provide'meanswhereby the sense of the direction of the transmitter can alsoaccurately and easily be found.

' Other objects-will be apparent from the to eliminate the simpleaerial-effect disturb:

- ing one or the other receiving minimum. The first-method has beenmostly used in 3 connection with immovable cross aerials or.

. cross loop aerials, and the direction was determined by means ofgoniometers- The second method was employed mainly in con junction withloop direction-finders capable 5 of being turned. Solely capacitivecouplings of the auxiliary aerial to thedirem tio'n-finder in the lattermethod'have been used because it was necessary-to eliminate everyadditional coupling coil in order not p 40 to displace the receivingminima,

The working and elie'ctof both mentioned ,methods are inaccurate. Thegoniometer' direction findershave many windings pointing to themagnetic'field and by these windings a minimum results which in generaldoes not coincide with the real minimum. Besides the goniometerarrangements always require several circuits by which the receivingeffects resulting from the magnetic- 5 field and the electric field arecombmed, so

that an alteration of; one of these effects alters the position of thereceiving K111111113 Furthermore the disturbing aerial e'fiect cannot beaccurately compensated-by reason of. the mentioned circuits. Thedirection.-

coiild be accurately determined by means of loop aerials andcapacitively coupled auxillary, aeri'als, but the working was difficultbecause every correction of the auxiliary aerial altered the syntony ofthe loop CIICHlt by reason of the unalterable coupling across thecondenser. Therefore this apparatus is very difficult towork.

Furthermore it is impossible to find the direction of-the transmitter bymeans of a loop aerial alone asthe axis :points to two opposeddirections.

The present invention relates to-a direction finder which eliminatesallthe mentioned. diffi cu-lties and guarantees an accuratedetermining-of direction.

. For an illustration of the manner of'practicing my invention,reference is tobe, had to the accompanying drawings, in which:

. Fig, 1 shows a diagrammatic view of the invention. Fig. 2 shows aschematic wiringdiagram of the manner in which the apparatus isconnected according to my invention. -Figs. 3-11 inclusive showschematicwi'r-' entire apparatus used in the practice-of my ing diagramsillustrating the operating principles of my invention, each-wiringdiagram being accompanied by curves-representing the energy received atdifferent angles of incidence of the waves on theap paratus shown in thewir ng d1agram'.--i;

Referring to Fig. 1, 1 is: 'ajsmall loop aerial of an area of about to1'square meter and capable. of being turned about a vertical axis. 2 isthe adjusting device and 3- a stationary scale for this 100 aerial whichis turned by means of a wire-rope extended by springs 5' and guided bypulleys 6 and 7. This construction has the ad vantage that the loopaerial can be placed at a suitable spot, for instance, in a screening or-shielding box on deck of a ship, whilst' theadjusting device 2 and thereceiving I apparatus arearranged-in a closed room underdeck. In orderto avoid, endfplay,

the wire-rope 4 is strained by means of the springs 5 led in parallel,so that the distance between loop aerial 1 and its adjusting device 2cannot cause wrong readings from the scale 3. The receiver is shownunder the 'aeriaL 8 is the knob of the tuning condenser for the loopaerial wave;

on the right is the tunin knob 9' for the con ling reaction and on t 10left the tuningv kno 1'10 for the :auxiliary aerial 11. The auxiliaryaerial 11 itself is as'imple wire of 10 to 16 meters in length,fre'elyextended at a certain distance from the 100 for which afconnection'termina 12.-is arranged on the left side of the receiver. Theconnection terminal 13lfor the earth wire of the auxiliary aerial 1 isshown below the terminal 12. The four vacuum. tubes 14 of the'radiofrequency amplifierare located in the middle of the .receiv'er.

between frame aerial 1' and auxiliary aerial 11. The receiver 1Sconnected to an audio V-frequency amplifierl'l', drawn on the'right Onthe left of the receiver there is a heterodyn-ing circuit 18, induc ofthe receiver.

tiVely coupled to the receiver. The .wave of this heterodyning circuitis adjusted by means of the handle 19 of a condenser and exchangeablecoils. The coupling of the heterodyning-circuit is regulated bya smallcoil 20 capable of .being turned'relative to fixed coil 20*. The audiofrequency amplifier is-supplied withone or more telephones 21 connectedthru one or more junction boxes 22. It is advisable to with a. furthertelephone for, ierudder, so

that, it need be, the ship can be steered by" means of this-telephone.The heating current for the vacuumtubes of all apparatus" is supplied byone 6 volt battery23'and another battery 24 of about 40 volts furnishesthe voltage for all plate-filament circuits. 1

-Figure 2 shows a schematic diagram of the' connections of thearrangement. In the middle of the windin s of the loop a coupling coil-40 is inserted, and the terminals. of the windings;are ,connectcd tothevariable tunin condenser 25.: The range 'of wave lengths can beincreased, for 1n-' stance, by means of a fixed condenser 26 which canbe connected in parallel to. condenser 25 by a switch 27. Fordetermining the direction of a transmitting station this circuit isfirst tuned. to that wavelength.- The loop aerial circuit is connectedto the radio frequency amplifier; The example of the schematicconnection shows three radio frequency vacuum tubes 28, 29, 30 and oneaudio frequency tube 31. The incandescent cathode 32 of the vacuum tube28 of the radio frequency amplifier is connected to the middle of theloop aerial coupling coil 40 across the coupling coil 20 of theheterodyning circuit 18. The grid 33 of the vacuum tube 28 of the radiofrequency amplifier is connected to one end of the frame winding 1,while the other end of aerial 1,

I The handle 15 of the switch for the auxiliary aerial. 11

is drawn below on the left, and on the right.

. is .the adjusting handle mm the coupling rovide' ships these-windingscanibe capacitively connected and regulated across a double variable r'otatable condenser 34 either' to the plate 35 of the vacuum tube 28 orplate 36aof-the tube 29. This double variable rotatable condenser 34regulates the couplingreaction as this reaction included in the givencon-- I .is increased. 011' the other hand, the cou-" pling reaction isdecreased, if acc'prdingto the changeable connection the loop circuit isconnected to the plate 36 of the vacuum tube 29, as these circuits areequi-phased. This alread known method has the great advantage t at thehighest degree of sensi tiveness and selection-is attained by using thecoupling reaction for reducing the damping and for amplifying the radiofrequency, because the loop circuit can be practically. considered" asufiicientl'y'. symmetricalar rangemeiitwith regard to, disturbingaerial currents. A further amplification can be attained bycoupling thereceiver with an audio frequency amplifier 17 by1means of transformer37. Furthermore it is advisable to use a. heterodyning circuit 18, asthe 'heterodyne 'm'ethodgenerates a beat-tone in case of undampedoscillations, so that the loop aerial circuit can be accurately tuned tothe receiving wave. The

- receiving energy of spark transmitters which is very small when theloop -aerialis adjusted to the receivingIminimum, is very much amplifiedthe application of the heterodyne method; The auxiliary aerial 11 servesfor correcting the receivin minima and also 'for producing a cardioihaving but one meamng. This auxiliary aerial has a" subdivided coil 38connected therewith by which the coeflicient ofcoupling with coil 40 canbe altered. The condenser 41 can be put in circuit by means of theswitch 42 in order to tune the auxiliary aerial 11 for producing the,cardioid. This syntony increases the receiving effect-of the auxiliaryaerial which l can be of small dimcnsions. This cardioid can also beproduced by means of an untuned but larger auxiliary aerial. The doubleI sided "minimum canalso be corrected by means of a small tunedauxiliary aerial if a. loose'coupling is employed. The trans ferenceofenergy from the auxiliary aerial '11 to the loop'circuit is regulatedfrom one maximum coefficient-10f coupling across a. y

minimum to a second maximum turning the couplmg 0011,40. These couplingmaxima have opposite phases. Instead of alter- 'by the opposite.

ing-the coefficient of coupling for instance by means of a coil' capableof being turned,-

the 'damping of the auxiliary aerial can be altered by means'of aregulatingresistance.

In this case a reversing switch is necessary reactions, as for instance,alterations of sy-n-' tony, decompositions of waves and similarprocesses. Therefore, the present invention employs a-very loosecoupling between auxihary aerial 11 and loop aerial 1. The anxiliaryaerial is chosen rather large so that it supplies the loop aerial withsuthcient en-' ergy in spite of loose coupling. In order to be able tofind the direction of a transmitter, the receiving operator must knowexactly that 'position of the coupling coil 40 in which practically noenergy is transferred-from the auxiliary aerial 11 to the loop aerial 1This position of the-coupling coil 40 is marked by zero on the scale 43.

The phase of the transferred energy .for all positions of the couplingcoil on the one side of tlie zero-position is the opposite of that forthe positions onthe other side. Ac-

cordingly, the coupling zero is the turning point of the cardioid. Thiszero-position of the coupling coil40 difi'ers from that for [anotherreceiving wave 'or another distance of the transmitter. In order toavoid mistakes in using the direction finder according to the presentinvention, that position of the coupling coil 40 which corresponds tothe coupling zero is determined by means of ahead telephone and then thepointer (not shown) on the axis of revolution of'this coil which isadjustable, is put on the zero point of the scale 43. This zero-pointthen represents the turning point of the cardioide.

Referring to Fig. 3 the wave front W'F is assumed to be perpendicular tothe ground and the windings of the loop aerial L are symmetricallyearthed. The arrow S points in the direction ofwave propagation. Thisfigure represents the simplest condition which occurs but infrequently.The diagram of the receiving characteristic here is a perfect'lemniscate. This diagram is ob- -tained by plotting the energy receivedby the loop- L at each angular direction of propa- LQtIOIIOf theincoming wave, the line AB representing the axisof the loop. Any linedrawn from the point 0 to the curve 100 represents the energy receivedby the loop when the direction'of wave propagation is parallel to thesaid line. It will be seen that the maximum energy is received when thedirection of wave propagation is at rlght angles to the axis ofthe loopand that no I In'Fig. 4 thewavcenergy induced in the loop when the di-'rection of wave propagation is parallel to I the axis of the loop. I

' Thus in this case the axis of the loop will accurately point in thedirection of the transmitter whenat the condition of zero energyreception in the loop. a a front WF is again vertical, bnt the'loopwinding L is unsymmetrically earthcd. The arrow S again points in thedirection of 'wave. propagation. v

The diagram of the resultantrecei'ving characteristic is represented at200, the line C--D representing the axis of the loop Circle 201represents the energy received in the loop, due to the so calledaerialef:

fect., that is, the energy duetothe unsyrnmetrical grounding of loop L.Curve 202 represents-the energy received in the loop due to pure loopeffect as in Fig. 3. The

phase of the energy due to the aerial effect is 90" from the electricfield of the income ingwaves-whilethe phase of the energydue to the loopeffect is. either 90 or 270 from.

the phase of the electric field of the incoming waves, depending onwhich side of the axis CD the transmitter is located.-

So, therefore. on one side of the axis CD the energies add, since theyare in phase and on the other side of the axis (1 -1). they oppose,since they are 180v out of phase.

Combining the curves 201 and 202 we obtain-curve 200 which representsthe resultant energyreceived in the loop.

It will be seen that lines OE and OF which represent the directions ofthe wave propagation which give minimum energy reception are both atangles to the loop axis C D which line. C- D should be the direc-' tionof the wave propagation giving a mini mum in the loop if the directionfinder is to be accurate. Therefore, inthis arrangement both directionsof minimum energy reception are inaccurate.

, In Fig. 5 the loop aerial L is shown symmetrically grounded but thewave front VVF is at an angle to the direction of'wave propagation shownby arrow Sand also at'an angle to ground. Such inclinations occur forinstance, if.tl1e electric wave passes from water to land. Theinclination can, for instance beproduced by absorption by the earth.This absorption is greatest near the ground and less in increasingheight. The

same effect occurs with ships if the waves "cdect on the loop since theloop is assumed to be symmetrically grounded. But the horizontalcompoiient, due to the axial breadth or length of the loop produces aiiaerial ef-:'

in Fig. 3. It will be easily seen that the phase of the energy'due .tothe loop efiect is 90, or 270 different in phase fromthe.

electriclield of the incoming waves do ending on which side of the axisG-I the transmitter is located, while thephase of the energy due toaerial effect of the hori zontal component is 90 or 270 difi'erent y inphasefrom the electricfield of the incomplaneof the loop the transmitteris 10- 0-cated. Since these two energies are either in phase of 180-outvof phase, it is-easy to add theireifects when. in phase and tosubtract when out of phase to produce the lemniscatel300' whichrepresents the resultant energy received in the loop L. Lines OI'and OJ-represent the directions of wave propa-- gationgiving zero energy to theloop and itis seen that these directions are both displaced from theaxis G--H of the loop L.

it This casealso shows that the axis of the loop L does not pointaccurately to the trans-.

mitter at either position of zero or minimum energy reception in theloop.

Fig; 6 shows an asymmetrically .earthed loop aerial L and an inclinedwave front WF, the arrow- S representing the direction of Wavepropagation. Curve 402 represents the energy due to the aerial effect ofthe vertical component of the inclinedwave. Curve ,403 represents theenergy due to the aerial effect of the horizontal component of theinclined wave. Curve 404 represents the resultant of these two.energies. ,Curve 401 represents the energy due to the pure loop eflec-t.Curve 400-represents the resultant energy due to all the combinedeifects and is obtained by-combined curves 404 and 401. Since all-ofthese energies are-either 90 or 270 out of phase with the incomingwave,-

they either directly add or oppose depend- I ing on the position of thetransmitter with respect to the loo Lines ON and SP represent thedirections of wave propagation giving zero energy to the loop and it isclearly seen that these directions are displaced from theaxisKM of theloop L.

Therefore, also in this case at both positions of zero energy reception,the axis of the loop Ldoes not point in the true direction of thetransmitter.

Fig. 7 shows an asymetrically earthed loop aerial L and a vertical Wavefront WF,

the direction'of propagation being represented by the arrow S. Acompensating unis coupled to loo mg wave depending onwhich side of thedirectional auxiliar aerial 510 is used and I by the'variable coupler511 composed o coils 512' and 513., This drawing may be compared withFigure 4 in which the aerial effect was notdirective and had the phase90 relative to the incoming wave. Inorder to compensate this effect, thecouplingbetween loop aerial 'L and that the auxiliary aerial ,510induces an effect-in the loop'L equal to the above aerial eifectbut withthe phase 270. Hereby the disturbing aerial effect-is compensated forall directions and the result is a perfectly symmetrical lemniscate 500and two exactly auxiliary aerial 510 should be so adjusted pointingmmima OR and OS coinciding with the axis RS of loop L. It is obviousthat in the case of vertical wave .front the asymmetry of the loopaerial can very easily and very accurately becompensated by the specialauxiliary aerial. Fig. 8 can be compared with Figure 5. It

shows a symmetrically earthed loop aerial L andan inclined Wave front WFand the arrow S pointin in the direction of wave propagation, as in Fig.5. The one receiving-mmimum has been made sharp and exact by means of anauxiliary aerial 610. As

in Fig. 5 the aerial effect caused by the horizontalcomponent of theinclined electric field has the shape of a lemniscate 601. If anelectro-motive force,'which has the same value as'the maximum voltageinduced in the loop due to the aerial effect of the horizontalcomponentofathe inclined electric field but'which has a 90 phaserelation to the incoming. electric wave. is transferred from theundirectional auxiliary aerial '610 to the loop aerial L, this effectdue to auxiliary aerial 610 and represented by curve 602 is combinedwithflthe aerial efiect illustrated by curve 601 to form a cardioid 603.This transfer of energy from the unidirectional auxiliary aerial 610 tothe loo aerial L is accomplished by means of varia le coupler 611 wwhich illustrates theflenergy induced in loop L due merely. to loopeffect to give curve 600 which represents the resultant of all thecombined energies received by the loop L. As 'shown the direction T0 ofzero energy reception coicides with the axis TU of the ich comprisescoils 612 and 613. v Curve 603 is'then combined with curve 60.4

loop L. This shows that the axis of the loop will point accurately tothe transmitting stas be obtained, the sense of 'the'coupling betweencoils 612 and 613 may be reversed,

care being exercised to keep the same coefficientof coupling. The caseillustrated by ter on the right side of the loop L can also Fig. 8 isthe one which occurs most in pracaerial. L and the resulting diagramaccuthe direction of wave propagation.

tice as the .loop aerials are constructed. as nearly symmetrical aspossible. and the disturbing aerial effect is caused chiefly by anunhomogeneous inclined electric field.

' Fig. 9 illustrates the case of an asymmetrt cally earthed loop aerialL,WF*representing'an inclined wave front and the arrow S diagram of theasymmetrically earthed loop* aerial -L in a position at right angles tothe positions shown in the prior figures. 'Its diagram is the smalllemnis cate' 801, the.energy induced-in theloop L having the phase 90 or270 with respect to the incoming wave depending'on' which. side ofthe-loop 1 'axis. ab the transmitter is located. The

effect of tuned auxiliary aerial 810-is the transference of energy ofapproximately the phase 270 to'the loop circuit by means of coils 812and- 813 of variable coupler 811. The phase can always be ad ustedexactly to 270 by means of the tuning condenser 814 of the auxiliaryaerial 810 by adjusting this condenser either larger or smaller, as re-"quired by resonance The amount of coupling between coils 812 and 813 isso chosen that the voltage induced inthe' 0011 813 is equal to themaximum voltage induced in the loop aerial L, that is, the voltage'lnduced in the loop L when the plane of the loop lies in the directionof the transmitter.

The resultant is a cardioid 800 pointing'to rection. of the transmitteris given the transmitting station. The ointer .815 on the movablecoilvof the varia le coupler- 811 at the time points to'a color, for in.stance, red on a fixed scale 43 (see also Fig. 2). The adjusting device2 of the. frameaeriall (Fig. 1) has mounted thereon a red arrowand agreen one. If the greatest audibility is obtained when the pointer 815is on the red marked part of the scale 43, {She (111- y t c red arrow onthe adjusting device 2 (Fig. 1).

It is thus seen that maximum audibility is obtained when the axis of theloopiL coincides with line 0-?) and the planeof the 100 points in thedirection Q-X.

ig. 11 shows a case similar to that of Figure 10, the sense of couplingbetween coils 812 and 813 being reversed. So thecardioid points to thedirection OY opposed to that of the transmitter, that is, the receivingisnearly equal to zero. The receiving operator sees from pointing ofpointer 815 to the green color that this-color is out of the questionfor the reading of the real direction.

The Figs. 3 to 11 are constructed theoretical examples for the mostfavorable casesinthat the phases of the energy received due to the loopeffect and due to the aerial effect are exactly 'or 270 "-diiferentinphase from the field of the transmitter. Of course, small differencesof phase occur in practice for different processes, but these.difierences do not materially alter the above described examples. It isonly necessary .to alter the phase, for instance, byv correcting thesyntony of the loop aerial or auxiliary aerial. The minima of thelemniscate notdete'rmining the real direction are furthermore altered bythesedifi'erences of phase, small in comparison with 180, that --is,these minima are in practice mostly unsharp.

It may be seen from the receding that the ship direction-finder acc'oring to thepresent invention is a simple and perfect apparatus.

As the receiving vacuum tubesworkcwith dampin reduction and couplingreaction, the audibility is as great as possible. The working of ,theapparatus is verysimple as only one auxiliary aerial is used. ,Thelemniscate' can be corrected b means of this untuned auxiliary aerialiit is very loosely eoupled to the frame aerial. The cardioid can begenerated by means of the tuned auxiliary aerial.

Having described. my invention, What I claim is: I Y I 1. In adirectional antennasystemfa nondirectional antenna and a rotatabledirectional antenna, variable coupling means for said antennas foradjusting the coeflicient and sense of. coupling between said antennaeto obtain a true pointing minimum at any desired wave length,'indicatinglmeans .fo'r said rotatable antenna and indicating means forsaid coupling means cooperating with said first named indicating meansfor indicating the true pointing minimum.

2. In a directional antenna system, a rotatable directional antenna anda separate non-directional -antenna, variable coupling -means for said,antennae'for adjusting the coeflieient and "sense of coupling betweensaid antennae to obtain atrue pointin minimum at any'wave-length'andadjusta leindicating means on said coupling means for'indicating thecoupling between said antennae 12H for'any wave length, and indicatingmeans on said rotatable antenna cooperating with said firstnamedindicating means to denote the true. pointing minimum... 1 V I 3. In adirectional antenna-system,- a di- 12 rectional antenna and. anon-directional an: 1 tenna, variable coupling -means forsaid antennaefor varying the cOefticientand. sense of coupling between them,means-tier rotating said directional antenna andindicating v .means forindicating the position of said directional antenna, indicating meansfor said variable coupling means for indicating thecoefiicient and senseof coupling between' said antenna, and meansv comprisin correspondingscales associated with said 1ndicating means'to determine th e.r'elationbetweenthe position of the'd-irectional antenna and coefficient andsense of coupling for the true pointing minimum. 4! In a directionalradio system, a nondl-rectlona'l aerial, a'loop aerial and 'means 1 forloosely'coupling said non directional aerial to said loop aerial, a is(plurality of tubes in cascade connected to sai loop, means fordirection of said system, for said antennas for adjusting thecoefiicient and sense of coupling between'saidantennae to obtain a truepointing minima at any desired Wavelength, indicating means for saidrotatable antenna, and indicating means for said coupling meanscooperating with said first named indicating means to indicate the truepointing minimum.

9'; The method of radio direction find- '.ing' with a directional loopaerial and a back coupling said tube circuits to'saidloo'p,

said means comprising-variable and selective condenser means foradjustably connecting said back coupling means to either of two Y forcoupling said'non put circuitsofisaid tubes.

of the .plate circuits of said tubes.

5. ,In a directional radio system, anon--- a'erial and means rectionalaer al to said'loop, said means comprislngmeans tor directional aerial,a 1005 1 varyingfthe coefiicient and sense of coupling between saidaerial s, a lurali'ty of vacuum .tubes connected in casca e to said loopaerial,

separate non-directional aerial which con-s sists 1n loosely couplingthe non-directional aerial to the directional aerial, tuning the loopaerial to the desired wave length, com

bining the loop receiving efiects with a small component from saidnon-directional aerial while in an untuned condition, determining thecoupling necessary to produce substan- .with a directional loop aerialand a separate means for back coupling said tubes to said means foradjustably' connecting said back coupling meansto either of two of theout- 6. In a directional radio system, a nondirectional aerial, a aerialand means 'for coupling said non-' irectional aerial to said loop, saidmeans comprising a variable loose coupling having a coll 1n the antennacircuit and a coil connected. substantially- 40 midway between theendsof said ,loop,.an amplifier circuit comprising a plurality of vacuumtubes in cascade the input circuit of said feed back to'either said amlifier being connected to'the central point 0 said loop;and to one endof'the loop, 'a'feed' back connection connected to the other end ofsaidloop comprising variable and selective condenser means forconnecting of two of the plate circuits of said tubes.

7. r In a directional antenna system, a rotatable directional antenna, anon-directional n enna, means comprising a. variable coupling betweensaid antennae for obtaining a plurality of sharply defined minima, andmeans, including an indicator on said rotata-. ble directional antenna,-and an indicator on said coupling means, so correlated to said firstnamed indicator'that the true pointing minimum minimum'may be read fromsaid-first named indicator, for indicating the true pointing 8. Inadirectional antenna system anondire'ctional antenna, a separaterotatable dinotional-antenna, variable coupling means including meansfor rotating the sense of tube circuits'to said loop,'said .meanscomprlsing, var1able"and selective condenser directionalantenna looselnon-directional aerial loosely coupled thereto which consists incombining the loop receiving effects with a small component from saidnon-direction aerial while in an untuned condition and determining thecoupling necessary to produce substantially perfect nullpoints,'substantially tuning the non-directional aerial to secure acardioid directionalsystem and alternately changin the direction ofcoupling to determine t e sense of direction.

11. A method of radio direction finding with adirectional loop and aseparate noncoupled thereto which consists in 'establis ing a minimumcoupling between the loop and the non-directional antenna, adjustingsaid minimum to produce substantially perfect null points for a givensignal, substantially tuning the non-. directionalaerial to secure acardioid directional system, varying the coupling and reversing itsdirection to determine the sense of direction.

i 12. In direction finding the method of correcting deviation of .thenull points caused by a distorted wave front on'a loop aerial havingappreciable width which consists in tuning the loop aerial to thedesired wave length, supplying energy from an auxiliary aerial while inan untuned condition and combining-enough of said energy with the energyinduced in said loop aerial by said distorted wave front to shift one ofthe null points of the loop energy curve'to a position along the axis ofthe loop.

' 13. The method of radio-direction finding with a loop aerial ofappreciable width in which out of phase currents are caused by adistorted wave front-which consists in, tuning the loop aerial to thedesired-wave length, supplying energy from an auxiliary non-directionalaerial 'while in an untuned received.

14:. In a directional antenna system, a loop aerial COIIlPIlSlllfI apair of electrically equal portions. a connection between said portions,

a rotatable inductance in said connection, a non-directional aerial,means for coupling said non-directional aerial to said loop aerialcomprising an inductance in said non-directional aerial coupled to saidrotatable inductance, tuning means for said loop aerial, an

amplifier system comprising a plurality of impedance coupled vacuum tubeamplifiers in cascade arrangement, a connection between the mid point ofsaid rotatable inductance and the filament electrode of one of saidvacuum tubes, a COIlnOQiZlO'libQtWGEIl one end 0t said loop aerial andthe gridelectrode oi said last named tube, capacit ve means for couplingthe other end of said loop aerial to the plate electrode of one of saidvacuum tube amplifiersfa local oscillatoigcoupling means between saidoscillator and said 100]) circuit and indicating means .associated'with'.said amplifier.

AUGUST LEIB.

CERTIFICATE OF CORRECTION.

Patent 'No. l, 685. 821.

It is hereby "above numbered patent requiring correct 'word valves' read"values"; and that Granted October 2, 1928, to j AUGUST LEIB.

certified that error appears in the printed specification of the ion asfollows: the said Letters Patent should be read Page 2, line 76, for thewith this correction therein that the same may conform to the record-oithe case in the Patent Oiiice.

Signed and sealed this. 7th day of May, A. n. 1929.-

(Seal) Mr]. Moore, Acting Commissioner of Patents.

